Bazı amfifilik enansiyomerlerin ve rasemik karışımlarının miselleşme termodinamiği

This thesis deals with the micellization process of the aqueous solutions of amphiphilic enantiomers (AEs) and their racemates as hydrogenated and partially fluorinated esters of alanine and serine, which are L/DL-alaninehydrochloride dodecylester (L/DL-ADDE), L/DL-serinehydrochloride dodecylester (L/DL-SDDE), L/DL-alaninehydrochloride 1H,1H,2H,2H-perfluorooctylester (L/DL-APFOE) and L/DL-serine hydrochloride 1H,1H,2H,2H-perfluorooctylester (L/DL-SPFOE). The thermodynamic, surface, volumetric and the structural properties of all these systems in pre-micellar and post-micellar regions have been investigated via electrical conductivity, surface tension, density, dynamic light scattering (DLS) and scanning electron microscopy (SEM) measurements.Krafft temperatures and critical micelle concentrations (cmc) of all systems were determined from the electrical conductivity measurements. The values of partially fluorinated, DL/L-APFOE and DL/L-SPFOE, amphiphiles were found to be markedly higher than those of the hydrogenated ones, DL/L-ADDE and DL/L-SDDE. In addition, remarkable differences in the cmc values of the chiral and racemic partially fluorinated amphiphiles were observed where the amphiphiles with serine head groups had larger cmc compared to that of alanine. The obtained standard Gibbs free energy change of micellizationshowed that the micellization process was energetically favored. The calculated standard enthalpy and entropy changes of micellization showed that micellization process was entropy-controlled at low temperatures and enthalpy-controlled at high temperatures for all systems.It was observed that the values of DL/L-ADDE, DL/L-SDDE, DL/L-APFOE and DL/L-SPFOE obtained from the surface tension measurements were smaller than those of conductivity measurements. For all systems, the values of racemic mixtures and L-enantiomers were almost the same within the error limits. It was observed that maximum surface excess concentration values decreased and minimum area per head group of the molecule at the air-water interface values increased with the increase in the temperature. However, there was no significant difference in the maximum surface excess concentration and minimum area per head group of the molecule at the air-water interface values of enantiomeric and racemic forms of the esters. It was observed that the partially fluorinated esters reduced the surface tension more than hydrogenated esters. Furthermore, the standard Gibbs free energy change of adsorption indicated that the adsorption of our systems at the air/water interface was spontaneous. Besides, it was found that the standard enthalpy change of adsorption was positive for hydrogenated dodecyl ester while it was negative for partially fluorinated octyl esters. The calculated standard entropy change of adsorption was found to be more positive than the standard entropy change of micellization for all of the systems.From the density measurements, it was observed that both partial specific volumes of monomer and micelles, apparent molal volume of monomer at infinite dilution and apparent molal volume of micelle values increased with the temperature. In addition, it was also found that the values of partial specific volume and apparent molal volume of micelle were significantly higher than those of partial specific volume and apparent molal volume of monomer values for each temperature. Furthermore, variations of volume change upon micellization with temperature exhibited considerably different behavior for the hydrogenated systems as compared to the fluorinated systems.Finally, from DLS and SEM investigations, it was found that all the hydrodynamic radii of the racemic mixtures and the L-enantiomers were almost the same. In addition, we observed that the hydrodynamic radius values of SPFOE and APFOE systems were markedly higher than ADDE and SDDE systems. The SEM images indicated that the micelles of our systems were nearly spherical in shape.